It is becoming increasingly commonplace to use models that simulate, or give an indication of, the behaviour of a system. A system can be considered generally as a collection of hardware, software, people, facilities, and procedures organized to accomplish some common objectives. A model can be thought of generally as a physical, mathematical, or otherwise logical representation of a system, entity, phenomenon, or process. The use of models is of particular importance in significant engineering projects, such as designing an aircraft, where the resources and risks involved are considerable. In such projects a mathematical model of an engineered system is normally used to provide a representation of the behaviour of the system, usually using computer-based modelling tools.
Unfortunately, the efficacy of system models is variable because it is determined by various factors. The difficulty of generating mathematical models has been well documented, see, for example, “Evaluating the Efficacy of Mathematically Modelling the Behaviour of Engineered Systems” Thesis submitted for the degree of Doctor of Philosophy, University of Newcastle upon Tyne, Faculty of Science, Agriculture and Engineering, 2006, currently available at http://www-staff.iboro.ac.uk/˜ouer/, the contents of which are hereby incorporated by reference. As discussed in that thesis, the accuracy of mathematical models is variable and it is desirable to have an indication of the overall efficacy of a given systems model.